Can I sue my husbands mistress for emotional distress or at least the money he spent on her?

It is very unlikely that you can sue your husband's mistress for emotional distress.  There are two torts involved - Intentional Infliction of Emotional Distress (IIED) and Negligent Infliction of Emotional Distress (NIED).  IIED requires as an element proof that the alleged conduct was "extreme and outrageous".  The phrase "extreme and outrageous" is a legal term that is defined by a particular state's common law (prior appellate decisions on the issue).  A spouse cheating on another spouse is not uncommon.  Although perhaps immoral, an affair is not so uncommon as to be extreme or outrageous.  As a result, you most likely do not have an IIED claim.

The tort of NIED is a negligence-based claim.  As with any negligence-based claim, NIED requires as an element proof that your husband's paramour owed a legal duty of care to you.  I am not aware of any court in the United States that has held that a cheating spouse's lover owes a duty of care to the non-cheating spouse.  As a result, it is highly doubtful that you have a NIED claim.

Please keep in mind that I am a Maryland divorce lawyer, and I have not done legal research specific to the laws of your state.  However, based on my experience and knowledge of the law, I would be surprised if you have any civil claim for damages against the paramour.  I believe your best course of action is to find divorce lawyers from your state who can help you end the marriage on the grounds of adultery.